Businesses and governments which provide the public specialized documents such as bank checks and drafts, traveler checks and currency expend substantial effort to assure that such documents meet certain quality standards. For example, for various reasons such as aesthetics, guaranty of authenticity of origin and genuineness of the document it is highly desirable for government agencies and businesses producing such documents to prevent the issuance of imperfect or flawed documents.
To insure the production of unflawed documents manufacturers employ highly sophisticated printing techniques in the production of the documents. Also for security reasons most of these documents are printed with highly complex patterns using various types of inks and papers. However, even with the use of the most modern of printing equipment documents are occasionally produced that are flawed or imperfect and in general fail to meet predetermined quality standards.
Therefore, some form of quality inspection is employed by manufacturers to insure that flawed documents are detected to prevent their issuance to the public.
Until recently, all such inspection was done visually by human operators. As is obvious, visual inspection is slow, costly and prone to human error.
Lately, due to advancements in the state of the art, the inspection process has been automated.
Using optical scanning techniques, a test document may be compared with a master document stored in a computer memory to determine whether the test document meets the predetermined standards represented by the stored master.
The inspection is accomplished by means of a point by point comparison between the test document and the stored master document. The points on the test document are picture elements or pixels each of which is the smallest area on the document which the system is capable of resolving. The master document is stored in memory with each pixel encoded in digital form. The test document is scanned by electro-optical means which converts the pixels into coded form. Each pixel of the test note is compared to the corresponding pixel of the stored master note. If the pixels compare favorably to an extent which meet predetermined quality standards, the test document is deemed acceptable.
In such an inspection system the test document moves relative to the optical scanning means and the point by point comparison with the stored master document is made in real time. Thus, a basic requirement of such an inspection system is the registration of each pixel on the test document with its corresponding pixel of the stored master document.
A document inspection system utilizing a registration system similar to that discussed above is described in U.S. application Ser. No. 954,018, now U.S. Pat. No. 4,197,584, entitled Optical Inspection System For Printing Flaw Detection filed on Oct. 23, 1978, having the same assignee as the present application.
The present invention relates to a registration system for use with a document inspection system.